1. Field
Example embodiments generally relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus incorporating the fixing device.
2. Discussion of the Background
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having two or more of copying, printing, scanning, facsimile, plotter, and other functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of a photoconductor; an optical writer emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a development device supplies toner to the electrostatic latent image formed on the photoconductor to render the electrostatic latent image visible as a toner image; the toner image is directly transferred from the photoconductor onto a recording medium or is indirectly transferred from the photoconductor onto a recording medium via an intermediate transfer belt; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
FIG. 1 illustrates one example of such fixing device. As shown in FIG. 1, a fixing device 100R includes a fixing belt 101R looped across a heating roller 111R accommodating a heater 110R and a fixing roller 113R including an elastic layer 112R. A pressing roller 102R is pressed against the heating roller 113R via the fixing belt 101R to form a fixing nip 114R between the pressing roller 102R and the fixing belt 101R. As a recording medium 120R bearing a toner image is conveyed through the fixing nip 114R, the fixing belt 101R heated by the heater 110R through the heating roller 111R and the pressing roller 102R apply heat and pressure to the recording medium 120R, thus fixing the toner image on the recording medium 120R.
In order to heat the fixing belt quickly, the fixing belt may be formed into a circular loop and receive light directly from a heater and indirectly through a reflector. FIG. 2 illustrates a fixing device 200R incorporating such reflector. As shown in FIG. 2, a tubular thermal conductor 202R is disposed opposite an inner circumferential surface of a fixing belt 204R. A heater 201R is interposed between the thermal conductor 202R and a reflector 203R. The thermal conductor 202R receives light from the heater 201R shown in the solid line that irradiates the thermal conductor 202R directly and light from the heater 201R shown in the dotted line that is reflected by the reflector 203R onto the thermal conductor 202R. Thus, the thermal conductor 202R, heated by the light from the heater 201R that irradiates the thermal conductor 202R directly and the light from the heater 201R that irradiates the thermal conductor 202R indirectly through the reflector 203R, in turn heats the fixing belt 204R. Accordingly, the fixing belt 204R is heated quickly.
However, since the reflector 203R is a single planar plate, it reflects light emitted from an invariable heating span L of the heater 201R onto the invariable heating span L of the thermal conductor 202R in an axial direction of the fixing belt 204R. Accordingly, if recording media of various sizes are conveyed through the fixing device 200R, the invariable heating span L of the thermal conductor 202R may not be equivalent to the width of recording media of various sizes and therefore the recording media may be heated unevenly in a width direction thereof parallel to the axial direction of the fixing belt 204R, resulting fixing failure.
For example, as shown in FIG. 2, as a recording medium P1 having a width W1 is conveyed through the fixing device 200R, since the width W1 of the recording medium P1 is equivalent to the invariable heating span L of the thermal conductor 202R and the fixing belt 204R, the recording medium P1 is heated evenly throughout the width W1 thereof as shown in the line indicating the temperature of the fixing belt 204R.
Conversely, as a recording medium P2 having a width W2 is conveyed through the fixing device 200R, since the width W2 of the recording medium P2 is greater than the invariable heating span L of the thermal conductor 202R and the fixing belt 204R, both lateral ends of the recording medium P2 outboard from the invariable heating span L in a width direction of the recording medium P2 may be heated insufficiently, resulting fixing failure.
Additionally, as shown in FIG. 3, as a recording medium P3 having a width W3 is conveyed through the fixing device 200R, since the width W3 of the recording medium P3 is smaller than the invariable heating span L of the thermal conductor 202R and the fixing belt 204R, both lateral ends of the fixing belt 204R outboard from the width W3 of the recording medium P3 in a width direction thereof may be overheated because the recording medium P3 is not conveyed over both lateral ends of the fixing belt 204R and therefore does not draw heat from the fixing belt 204R. Accordingly, the fixing belt 204R may be subject to thermal damage and breakage.